A fortnight earlier, 143 people died when an earthquake hit Athens. Two weeks before that, a massive quake devastated Turkey; the death toll was a staggering 15 600. In all, more than 3 million people have died in earthquakes over the past 100 years.
More than ever before, the pressure is on for designers to make buildings earthquake-proof. An Ove Arup & Partners-designed convention centre in Osaka offers one solution.
Ted Piepenbrock is head of the firm’s seismic engineering group and led the team that designed the centre. He finds the death toll in recent earthquakes “completely unacceptable … There should not be a single loss of life.”
Piepenbrock is passionate about engineering buildings to save lives. “Deaths are caused by buildings that perform badly in earthquakes,” he says – and he is speaking from experience.
As an engineer working in the USA in 1989, he witnessed the largest earthquake to hit San Francisco this century. Fifty people lost their lives when a bridge collapsed. Piepenbrock says: “We knew that bridge would fail. We just hadn’t gotten round to upgrading it.”
A mammoth job
Six years later, Piepenbrock was in Osaka, facing a daunting task. Japan was still reeling from the biggest earthquake ever to hit the country just four months earlier. More than 6500 people died, and £1.22bn of damage had left Kobe, the town at the quake’s epicentre, in ruins. Osaka is only a few kilometres from Kobe.
Now nearing completion, the Osaka International Convention Centre stands 13 storeys high. Its top floor has a conference hall for 400 people giving panoramic views of the city. On its fifth and sixth floors, a cavernous convention hall, large enough to house 2800 people, will divide the building vertically, and 25 separate function rooms scattered throughout the remainder of the building will each accommodate between 10 and 1000 people.
A lack of space forced the design of the convention centre upwards rather than outwards, making it more likely to topple in an earthquake. To make matters worse, a public plaza had to be incorporated into the design, so the building had to be raised off the ground on legs. The resulting structure is rectangular in plan, measuring 90 × 60 m, and stands more than 100 m high.
The constraints imposed by the convention centre’s unusual layout created a problem for the designers. With the centre supported above the ground on slender legs, conventional earthquake design was inappropriate. Some radical thinking was needed.
The team – the first made up of non-Japanese seismic consultants to design a high-rise building in the country – came up with the unusual proposal of incorporating what Piepenbrock calls “the world’s largest shock absorbers” into the structure. The shock absorbers would help soak up the massive amount of energy released by an earthquake, energy that would otherwise cause the building to wobble, or even collapse.
The shock absorbers are used to cross-brace the structure. Six cores, one in each corner and one at the mid-point of each of the longer sides of the centre’s rectangular base, contain all the vertical structural elements that support the building’s weight. At every third floor, single-storey trusses span the cores. Intermediate floors are then either hung or propped from these trusses, which are further stiffened by hundreds of shock absorbers.
In an earthquake, these shock absorbers will soak up the impact by using its energy to deform their sacrificial steel core. All the shock absorbers would need to be replaced afterwards, but the building’s main supporting structure would be intact.
Piepenbrock had to be sure the radical scheme would work. He knew that if the building failed, lives would be lost. Careful analysis of the structure was needed. So, Piepenbrock turned to Ove Arup’s advanced technology group, which specialises in car safety. He used the team’s expertise, and advanced software usually used to analyse car crashes, to examine every structural component of the convention centre under numerous earthquake simulations.
Bringing building into the 20th century
These showed that the design would not fail and the building was approved by Japan’s special approvals commission, which must approve any structure more than 60 m high. Work started on site in November 1996 and the centre is on target to be completed by this Christmas.
Fortunately, the solution has yet to be tested in a real earthquake. But Piepenbrock is so convinced that the computer simulations are accurate that he is already working on an even larger scheme in Japan, using the giant shock absorbers to protect a football stadium.
The use of advanced automotive engineering techniques in seismic design has allowed Piepenbrock to advance the design of buildings that will prevent further loss of life. With these techniques, he says: “We’ve finally brought building into the 20th century.”